KR20070036117A - Method for implementing channel estimate in orthogonal frequency division multiplexing (ofdm) system - Google Patents

Abstract

A method for channel estimation in an Orthogonal Frequency Division Multiplexing (OFDM) system includes a method in which a transmitter determines a distribution density of pilot OFDM symbols according to a maximum Doppler frequency shift supported by the system, and determines a distribution density of the pilot OFDM symbols. Transmitting a pilot OFDM symbol and a data OFDM symbol on the basis; And a receiver estimating frequency domain channel information of data OFDM symbols according to the received pilot OFDM symbols. The present invention solves the large performance loss in high delay channels and problems in systems where the channel changes rapidly. The present invention provides superior performance of channel estimation even when the channel environment changes rapidly, improves the performance of high delay channels, makes the data communication system more suitable for changing environments, and more By exerting good performance, the data transmission efficiency of the system is increased.

OFDM symbol, transmitter, receiver, channel estimation

Description

Channel Estimation Method for Orthogonal Frequency Division Multiplexing System (METHOD FOR IMPLEMENTING CHANNEL ESTIMATE IN ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING (OFDM) SYSTEM)

FIELD OF THE INVENTION The present invention relates to orthogonal frequency division multiplexing (OFDM) techniques, and more particularly to a method for channel estimation in an OFDM system.

OFDM technology is one of frequency division multiplexing techniques for high rate data transmission services. Compared with conventional single carrier technology, OFDM provides higher spectral efficiency by using a simple equalization algorithm. On the other hand, bandwidth is saved because there is no need to assign a frequency guard band between neighboring subcarriers to avoid frequency interference, which has been adopted in conventional frequency division multiplexing (FDM).

Recently, OFDM technology has been widely used in communication systems and has been applied to the wireless LAN standard 802.11a and the fixed wireless access standard 802.16a. In addition, with respect to the 3GPP radio access network and the IEEE 802.20 physical layer, OFDM technology is being considered to build a mobile radio access system with high spectrum efficiency.

1 shows a networking diagram of a conventional frequency division cellular system. In this system, two radio network controllers (RNC), RNC1 and RNC2 are connected to the core network (CN), and some base stations (BS) are connected to one of the two RNCs, where BS1, BS2 and BS3 are It is connected to RNC1, BS4, BS5 and BS6 are connected to RNC2, and two mobile stations MS, MS1 and MS2 maintain a radio connection with the BSs. 2 is a conventional cell omni-directional antenna multi-mode, referred to simply as cell multi-mode. 3 is a conventional cell 120 degree directional antenna multiple mode, referred to simply as sector multiplexing mode. The data transmission technique using the OFDM technique has the following advantages.

1. Excellent robustness under multipath delay spread. As shown in Fig. 4, the time domain OFDM symbol includes two portions of a data portion and a cyclic prefix portion, wherein the cyclic prefix portion is generated by calculating the final portion of the data portion, as shown in the figure. The portion occupies the duration T _data , and the cyclic prefix portion occupies the duration T _cp . The robustness of the OFDM technique can be said as follows, compared to the OFDM symbol duration T _s , the conventional channel impulse response duration is very short and occupies only a very short portion of T _s , thus a shorter cyclic prefix. In other words, increasing T _cp completely eliminates interference between signals caused by multipath.

2. Excellent robustness under frequency selective fading. With redundancy solutions such as channel coding, OFDM techniques can recover digital signals carried by poor fading subcarriers.

3. Simple equalization algorithm. Since OFDM technology can transmit signals in the frequency domain and use simple multiplication to represent channel effects in the frequency domain, a simple tap equalizer can be used to equalize the signals in an OFDM system. .

4. Higher spectral efficiency compared to commonly used FDM technology.

Although a data transmission system using OFDM technology has the advantages described above, in order to realize the advantages in a real system, more specifically, to operate an OFDM system generally, frequency synchronization, symbol synchronization, frame synchronization, channel It is necessary to develop some key techniques such as estimation and equalization. This key technology is not only about the application environment of the system but also about the requirements of the network configuration of the system.

The purpose of channel estimation in the key description described above is that through channel estimation, the receiver can obtain frequency domain information of the channel to which the transmitter transmits data, and based on the frequency domain information of this channel, the receiver performs equalization processing. To get the data. Therefore, channel estimation is an important prerequisite for the receiver to obtain data accurately and effectively.

The IEEE 802.11a protocol provides a channel estimation technique. The frame structure of the 802.11a system is shown in FIG. Every frame includes a preamble, and a data OFDM symbol with an inconsistent length. The data OFDM symbol includes user data and signaling. The pilot subcarrier allocation solution of 802.11a is shown in FIG. In the physical layer selection solution of 802.11a and 802.16a, channel estimation uses the preamble. Specifically, since the receiver knows the date returned to all subcarriers of the preamble transmitted by the transmitter, according to the received preamble, channel conditions of all subcarriers of the preamble can be obtained, and the channel environment When this slowly changes, the channel conditions of all subcarriers of the preamble can be considered as channel conditions of corresponding subcarriers of OFDM.

In other words, the channel estimation solution provided by 802.11a is based on the channel condition of the data OFDM symbol being close to the channel condition of the corresponding preamble. When the channel environment changes rapidly, this approximation can cause big errors. In addition, the channel environment also changes with the relative movement between the receiver and the transmitter. Thus, the above solution is not effective for applying to a system in a rapidly changing channel environment. Since channel conditions in current mobile wireless communication systems are changing rapidly, it can be clearly said that this channel estimation solution provided by 802.11a is not suitable for mobile wireless communication systems.

In 802.11a, by introducing a pilot subcarrier, the channel change is tracked to correct the channel conditions of all subcarriers of the preamble, and the corrected channel conditions of all subcarriers of the preamble are compared to the subcarriers of the data OFDM symbol. Although intended to be taken as a channel condition, such correction does not reflect a rapid change in channel condition and causes significant degradation in performance.

In order to solve the above problem, a pilot subcarrier allocation solution of a time frequency grid has been proposed and shown in FIG. In this solution, the pilot OFDM symbols, or preambles, are evenly distributed over the time frequency plane. Using pilot OFDM symbols to track channel changes can partially solve the problem of channel changes.

Siemens has proposed 3GPP RAN1, which proposes a specific solution for assigning pilot frequencies based on channel estimation method and simulation results as well as time frequency grid mode. This solution uses twice-order one-dimension interpolation to obtain the data subcarrier channel conditions on the time frequency plane, first performing third-order Lagrangian interpolation over the time domain and then the frequency domain. The 7th Lagrangian interpolation is performed. Simulation results provided by Siemens show 0.5-0.7 dB performance degradation for the PA3, PB3 and VA30 channels and floor error at BLER = 0.13 for the VB30 channel. This means that for channels with large delays, Siemens' channel estimation solution has a significant degradation in performance.

In view of the foregoing, the present invention provides a method for channel estimation in an OFDM system to reduce performance degradation at a receiver while performing channel estimation.

The technical scheme of the present invention is described as follows.

Method for channel estimation in an orthogonal frequency division multiplexing (OFDM) system,

a. Determining, by the transmitter, a distribution density of pilot OFDM symbols according to a maximum Doppler frequency shift supported by the system, and transmitting a pilot OFDM symbol and a data OFDM symbol based on the distribution density of the pilot OFDM symbols; And

b. Estimating, by the receiver, frequency domain channel information of data OFDM symbols according to the received pilot OFDM symbols

It includes.

In step a, determining the distribution density of the pilot OFDM symbols according to the maximum Doppler frequency shift,

The number of data OFDM symbols between neighboring pilot OFDM symbols is given by

Determining according to,

Where n is the number of data OFDM symbols between neighboring OFDM symbols, T _d is the duration occupied by one data OFDM symbol, and f _{d , max} is the maximum Doppler frequency shift supported by the system.

Step b,

b11. Obtaining, by the receiver, a time domain channel response of the pilot OFDM symbol according to the received time domain pilot OFDM symbol;

b12. Extracting the time domain channel information of the pilot OFDM symbol according to the time domain channel response of the pilot OFDM symbol; And

b13. Estimating frequency domain channel information of the data OFDM symbol according to the time domain channel information of the pilot OFDM symbol

It includes.

According to the solution provided by the present invention, the distribution density of the pilot OFDM symbol is determined according to the maximum Doppler frequency shift supported by the OFDM system, and the receiver performs data OFDM symbol frequency domain channel information according to the received pilot OFDM symbol. Estimate In this way, good performance is achieved even in high latency and rapidly changing channel environments. The present invention improves the channel environment adaptability of the data communication system, improves the performance of the actual channel estimation in the OFDM system, and increases the data transmission efficiency of the system.

1 is a networking diagram illustrating a conventional frequency multiplexing cellular system.

2 is a schematic diagram illustrating a conventional cell omnidirectional antenna mode.

3 is a schematic diagram illustrating a conventional cell 120 degree sector antenna mode.

4 is a diagram illustrating an OFDM symbol.

5 is a diagram illustrating a frame of 802.11a.

6 is a schematic diagram illustrating a pilot frequency distribution of 802.11a.

7 is a schematic diagram illustrating a pilot grid mode.

8 is a schematic diagram illustrating a distribution relationship between a pilot OFDM symbol and a data OFDM symbol.

9 is a schematic diagram illustrating a structure of a pilot OFDM symbol.

10 is a schematic diagram illustrating a structure of a data OFDM symbol.

11 is a flowchart illustrating a process of a transmitter for transmitting an OFDM symbol.

12 is a flowchart illustrating a process of a receiver for receiving an OFDM symbol.

13 is a schematic diagram illustrating a number section of an OFDM symbol according to the present invention.

14 is a schematic diagram illustrating channel estimation and process in a receiver according to an embodiment of the present invention.

15 is a flowchart illustrating a process of channel estimation corresponding to FIG. 14.

16 is a flowchart illustrating another process of channel estimation.

17 is a simulation diagram for channel estimation performance under vehicle A channel at 30 km per hour and cutting path 32.

18 is a simulation diagram for channel estimation performance under vehicle A channel of 60 km per hour and cutting path 32.

19 is a simulation diagram for channel estimation performance under vehicle B channel of 30 km per hour and cutting path 160.

The present invention first sets the distribution density of the pilot OFDM symbol according to the maximum Doppler frequency shift supported by the system, and based on the distribution density of the pilot OFDM symbol, the transmitter transmits a pilot OFDM symbol and a data OFDM symbol. The receiver then performs channel estimation of the data OFDM symbol according to the received pilot OFDM symbol.

Hereinafter, with reference to the accompanying drawings and embodiments of the present invention will be described in detail.

First, the distribution density of the pilot OFDM symbol is determined according to the maximum Doppler frequency shift, i.e., the moving speed of the mobile station supported by the system. Similar to the prior art, the frame structure according to the embodiment of the present invention includes a pilot OFDM symbol and a data OFDM symbol, as shown in FIG. Determining the distribution density of the pilot OFDM symbols is to determine the number of data OFDM symbols between neighboring pilot OFDM symbols. The number of data OFDM symbols between neighboring pilot OFDM symbols depends on how rapidly the channel environment changes. More specifically, define the relationship between the maximum Doppler frequency shift f _{d , max} supported by the system and the maximum travel speed V _max supported by the system as follows.

Where f _c is the carrier frequency of the system and c is the speed of light. Generally speaking, the number of data OFDM symbols between neighboring pilot OFDM symbols satisfies the following conditions.

Provided that T _d is the duration occupied by the data OFDM symbols and n is the number of data OFDM symbols between neighboring pilot OFDM symbols.

The length of the pilot OFDM symbol is equal to or not equal to the length of the data OFDM symbol is the same as in the prior art. Similarly, it is similar to the prior art that both the pilot OFDM data and the data OFDM symbol include a cyclic prefix portion and a data portion, and the cyclic prefix portion is generated by cycling the last portion of the data portion. The length of the cyclic prefix portion is expressed as the number of sample points, and the length of the data portion is also expressed as the number of sample points. The structure of the pilot OFDM symbol is shown in FIG. 9, where N _{p , cp} is the length of the cyclic prefix portion, and N _{p , data} is the length of the data portion. The structure of a data OFDM symbol is shown in FIG. 10 where N _{d , cp} is the length of the cyclic prefix portion and N _{d , data} is the length of the data portion.

In general, the length of the data portion of the pilot OFDM symbol may be the same as or different from the length of the data portion of the data OFDM symbol. In order to save the system resources occupied by the pilot OFDM symbol, a solution according to an embodiment of the present invention is to make the length N _{p , data} of the data portion of the pilot OFDM symbol shorter than the length N _{d , data} of the data portion of the data OFDM symbol. Set it. In general, the two values N _{p , data} and N _{d , data} can be set to satisfy the following equation.

In general, the length of the cyclic prefix portion of the pilot OFDM symbol may be the same as or different from the length of the cyclic prefix portion of the data OFDM symbol. In order to improve the negative effect on the pilot OFDM symbol caused by the multipath delay, the solution according to the embodiment of the present invention is to calculate the length N _{p , cp} of the cyclic prefix portion of the pilot OFDM symbol by the cyclic prefix of the data OFDM symbol. Set the length of the part longer than N _{d and cp} .

Based on the above settings of the pilot OFDM symbol and the data OFDM symbol, the transmitter first generates a pilot OFDM symbol and a data OFDM symbol according to the cyclic and data portions of the pilot OFDM symbol and the data OFDM symbol, and then these 2. Multiplexing symbols in the time domain, and performing the same process as D / A conversion and transmitting the generated OFDM symbols. This transmission process is shown in FIG.

During reception, the receiver first samples the received electromagnetism signal and then demultiplexes the sampled data on the time domain based on the obtained time synchronization to form a time domain pilot OFDM symbol and a time domain data OFDM symbol. And then obtain a pilot OFDM symbol and a data OFDM symbol on the frequency domain, and then estimate frequency domain channel information of the data OFDM symbol based on the pilot OFDM symbol, and finally based on the frequency domain channel information of the data OFDM symbol. Recover the transmitted data OFDM symbols using channel equalization. This receiving process is shown in FIG.

In the process of handling the received signal, while estimating the frequency domain channel information of the data OFDM symbol based on the pilot OFDM symbol, the receiver may adopt two solutions in addition to the existing solution. The first solution is as follows: First, the receiver obtains time domain channel information of the pilot OFDM symbol based on the received pilot OFDM symbol, and then uses an interpolation algorithm, according to the time domain channel information of the pilot OFDM data OFDM symbol. Estimates the time domain channel information of < RTI ID = 0.0 > and then < / RTI > The second solution is as follows:

First, the receiver obtains time domain channel information of the pilot OFDM symbol based on the received pilot OFDM symbol, and then obtains frequency domain channel information of the pilot OFDM symbol based on the time domain channel information of the pilot OFDM symbol, and then interpolates. Using the algorithm, the frequency domain channel information of the data OFDM symbol is estimated according to the frequency domain channel information of the neighboring pilot OFDM symbol.

To describe these two processing schemes, numbers are assigned to transmitted OFDM symbols according to the following rules.

Number of Pilot OFDM Symbols: The number of pilot OFDM symbols is allocated according to the time sequence in which they are transmitted, and the smaller number of pilot OFDM symbols transmitted earlier is assigned.

Natural number of n data OFDM symbols between neighboring pilot OFDM symbols: A natural number of 1 to n is taken, but the smaller number is given to the pilot OFDM symbol transmitted earlier.

Number of data OFDM symbols: First, multiply the number of pilot OFDM symbols that are neighbors but transmitted before the data OFDM symbols by the number of data OFDM symbols between neighboring pilot OFDM symbols, and then the data between neighboring pilot OFDM symbols Add the natural number of the OFDM symbol.

According to the above rule, a part of the number of OFDM symbols is shown in FIG. Where k-1, k, k + 1 and k + 2 are pilot OFDM symbol numbers; n * (k-1) +1 ..., n * (k-1) + n is the number of data OFDM symbols between pilot OFDM symbol k-1 and pilot OFDM symbol k: n * k + 1 .. n * k + n is the number of data OFDM symbols between pilot OFDM symbol k and pilot OFDM symbol k + 1; n * (k + 1) +1 ..., n * (k + 1) + n is the number of data OFDM symbols between pilot OFDM symbol k + 1 and pilot OFDM symbol k + 2.

)를 반송한다.Based on the above rules, the i th subcarrier of the k th pilot OFDM symbol carries a frequency domain signal Dk, i, and then the k th pilot OFDM symbol is a frequency domain signal sequence (

B) return.

A first channel estimation method in which time domain data OFDM symbol channel information is first obtained and then frequency domain channel information is obtained will be described in detail below. 14 shows a processing diagram of the first solution and FIG. 15 shows a flowchart.

Step 1501. According to the received time domain pilot OFDM symbol, a time domain channel response in the pilot OFDM symbol is obtained.

)인 것으로 가정하면, 고속 푸리에 변환(FFT)과 같은 푸리에 변환을 통해, 상기 수신된 주파수 도메인 신호 시퀀스(

)가 얻어진다. k번째 파일럿 OFDM 심벌에 의해 반송되는 주파수 도메인 신호 시퀀스는 (

)이기 때문에, k번째 파일럿 OFDM 심벌에서의 주파수 도메인 채널 응답은 (

)이고, 간단하게 표현하면 (

)이다. 얻어진 주파수 도메인 채널 응답 (

)에 대해 역 고속 푸리에 변환(IFFT)과 같은 역 푸리에 변화를 수행함으로써, k번째 파일럿 OFDM 심벌에서의 시간 도메인 채널 응답이 얻어지고, 간략하게 표현하면 (

)이다.The time domain signal sequence of the k-th pilot OFDM symbol received is (

Assuming that the received frequency domain signal sequence (i.e., a Fourier transform, such as a fast Fourier transform (FFT)

) Is obtained. The frequency domain signal sequence carried by the kth pilot OFDM symbol is (

Since the frequency domain channel response in the kth pilot OFDM symbol is

), In simple words (

)to be. Obtained Frequency Domain Channel Response (

By performing an Inverse Fourier Transform, such as an Inverse Fast Fourier Transform (IFFT), for a time domain channel response in the kth pilot OFDM symbol,

)to be.

Step 1502. According to the time domain channel response in the pilot OFDM symbol, time domain channel information of the pilot OFDM symbol is extracted, and the time domain channel information includes path delay, path fading, and the like.

Once the time domain channel response in the pilot OFDM symbol is obtained, it is necessary to analyze the information to obtain effective channel information in order to reduce noise and interference.

There are two ways to get effective channel information. One method is a simple truncation method, which can be used when the range of channel delay in a wireless transmission environment is known, and the other method is an adaptive extraction method of channel information.

)은 바로 절단되며, 절단 범위는 최대 지연의 대응하는 샘플 포인트보다 약간의 비트만큼 더 크며; 예를 들어, 절단 범위는 N'이고, N'≤N이다. 이 경우, k번째 파일럿 OFDM 심벌에서의 얻어진 시간 도메인 채널은 (

)이고, 여기서 제로의 수는 N_{p ,data}-N'이다. 적응성 추출 방법에 있어서, 시간 도메인 채널 응답으로부터의 기간 동안에 지속적으로 수신되는, 파일럿 OFDM 심벌의 시간 도메인 채널 응답 (

) 중 가장 강력한 경로가 효과적인 경로로서 선택되 고, 그 선택된 경로가 지속적일 필요는 없다. 예를 들어, 상기 기간 동안에 있어서는, (

)가 효과적인 채널 정보로서 선택될 수 있다. 상기 효과적인 채널 정보를 결정하면, 제로를 사용하여 파일럿 OFDM 심벌의 시간 도메인 채널 응답에서의 선택되지 않은 시간 도메인 채널 값을 대체한다.In a simple cutting method, the cutting range is determined based on the delay spread supported by the system. For example, assuming that the maximum channel delay is N sample points, the time domain channel response in the pilot OFDM symbol obtained in step 1502 (

) Is truncated immediately, and the truncation range is slightly larger than the corresponding sample point of the maximum delay; For example, the cutting range is N 'and N'≤N. In this case, the obtained time domain channel in the kth pilot OFDM symbol is (

), Where the number of zeros is N _{p , data} -N '. In the adaptive extraction method, the time domain channel response of a pilot OFDM symbol, which is continuously received for a period from the time domain channel response,

The strongest path of the) is chosen as the effective path, and the selected path need not be persistent. For example, during this period,

) May be selected as effective channel information. When determining the effective channel information, zero is used to replace the unselected time domain channel value in the time domain channel response of the pilot OFDM symbol.

In addition, the above-described adaptive extraction method can be simplified. For example, cutting can be used in this method to form an adaptive cutting method. The adaptive truncation method is as follows: First, the truncation length N 'is determined by analyzing successive time domain channel responses in the pilot OFDM symbol and taking the length of that region as N' to find the energy concentration region, The next time domain channel value before N 'is obtained and the non-selected time domain channel response in the pilot OFDM symbol, ie the time domain channel value after N', is replaced with zero. In this way, time domain channel information is determined.

Step 1503. Estimate time domain channel information of the data OFDM symbol by performing specific interpolation on time domain channel information of neighboring pilot OFDM symbols.

)를 얻으면, 데이터 OFDM 심벌의 시간 도메인 채널 정보 (

)를 추정하며, 여기서 s는 데이터 OFDM 심벌의 수이다.Time Domain Channel Information of Pilot OFDM Symbol

), Time domain channel information of the data OFDM symbol (

), Where s is the number of data OFDM symbols.

)를 사용하여

값을 추정할 수 있으며, 여기서 j는 이웃하는 파일럿 OFDM 심벌 사이의 데이터 OFDM 심벌들의 자연수이다.Specifically, (

)use with

The value can be estimated, where j is the natural number of data OFDM symbols between neighboring pilot OFDM symbols.

값을 추정하기 위해, (2l-1)차 라그랑즈 보간을 채택할 수 있다. 통상적인 추정 식은 이하와 같다:

To estimate the value, we can adopt (2l-1) th order Lagrangian interpolation. Typical estimation equations are as follows:

는 (k+m)번째 파일럿 OFDM 심벌의 i번째 샘플 포인트에서의 시간 도메인 채널 값이고,

는 (k*n+j)번째 데이터 OFDM 심벌의 i번째 샘플 포인트에서의 시간 도메인 채널 값이며, n은 이웃하는 파일럿 OFDM 심벌 사이의 데이터 OFDM 심벌들의 수이다.only,

Is a time domain channel value at the i th sample point of the (k + m) th OFDM OFDM symbol,

Is the time domain channel value at the i th sample point of the (k * n + j) th data OFDM symbol, and n is the number of data OFDM symbols between neighboring pilot OFDM symbols.

When first-order Lagrangian interpolation, ie linear interpolation, is performed, the above equation can be simplified as follows:

는 k번째 파일럿 OFDM 심벌의 i번째 샘플 포인트에서의 시간 도메인 채널 값이고,

는 (k*n+j)번째 데이터 OFDM 심벌의 i번째 샘플 포인트에서의 시간 도메인 채널 값이며, n은 이웃하는 파일럿 OFDM 심벌들 사이의 데이터 OFDM 심벌들의 수이다.only,

Is the time domain channel value at the i th sample point of the k th pilot OFDM symbol,

Is the time domain channel value at the i th sample point of the (k * n + j) th OFDM symbol, and n is the number of data OFDM symbols between neighboring pilot OFDM symbols.

Likewise, with the (2l-1) logarithmic Lagrangian interpolation, a typical estimate is:

는 (k+m)번째 파일럿 OFDM 심벌의 i번째 샘플 포인트에서의 시간 도메인 채널 값이고,

는 (k*n+j)번째 데이터 OFDM 심벌의 i번째 샘플 포인트에서의 시간 도메인 채널 값이며, n은 이웃하는 파일럿 OFDM 심벌들 사이의 데이터 OFDM 심벌들의 수이다.only,

Is a time domain channel value at the i th sample point of the (k + m) th OFDM OFDM symbol,

Is the time domain channel value at the i th sample point of the (k * n + j) th OFDM symbol, and n is the number of data OFDM symbols between neighboring pilot OFDM symbols.

Likewise, if you perform linear algebraic Lagrangian interpolation, or linear algebraic Lagrangian interpolation, the above equation can be simplified to:

는 (k+m)번째 파일럿 OFDM 심벌의 i번째 샘플 포인트에서의 시간 도메인 채널 값이고,

는 (k*n+j)번째 데이터 OFDM 심벌의 i번째 샘플 포인트에서의 시간 도메인 채널 값이며, n은 이웃하는 파일럿 OFDM 심벌들 사이의 데이터 OFDM 심벌들의 수이다.only,

Is a time domain channel value at the i th sample point of the (k + m) th OFDM OFDM symbol,

Is the time domain channel value at the i th sample point of the (k * n + j) th OFDM symbol, and n is the number of data OFDM symbols between neighboring pilot OFDM symbols.

)을 추정한다. 뒤이어 제로의 N_{d ,data}-N'를 가산하면, (

)가 얻어진다.Using any of the above formulas,

Estimate). Subsequently adding zero N _{d , data} -N ',

) Is obtained.

Step 1504. Using the time domain channel information of the data OFDM symbol, frequency domain channel information of the data OFDM symbol may be obtained.

)에 대해 IFFT를 실행하면, s번째 데이터 OFDM 심벌에서의 주파수 도메인 채널 응답 (

)이 얻어진다.Specifically, the obtained time domain channel response of the sth data OFDM symbol (

IFFT is performed on the frequency domain channel response (s) in the sth data OFDM symbol.

) Is obtained.

According to the second channel estimation method, first, frequency domain channel information of a pilot OFDM symbol is obtained, and frequency domain channel information of a data OFDM symbol is obtained. The flow diagram is shown in FIG. 16 and has the following steps:

Step 1601. According to the received time domain pilot OFDM symbol, a time domain channel response in the pilot OFDM symbol is obtained.

This step is the same as step 1501.

Step 1602. According to the time domain channel response in the pilot OFDM symbol, time domain channel information of the pilot OFDM symbol is extracted; The time domain channel information includes path delay, path fading, and the like.

This step is the same as step 1502.

Step 1603. Obtain corresponding frequency domain channel information of the pilot OFDM symbol according to the obtained time domain channel information of the pilot OFDM symbol.

Step 1604. Frequency domain channel information of the data OFDM symbol is obtained by performing interpolation on the frequency domain channel information of the pilot OFDM symbol.

In step 1604, the interpolation is a (2-1) order Lagrangian interpolation. In addition, by taking the frequency domain channel information of the pilot OFDM symbol directly as the frequency domain channel information of the data OFDM symbol adjacent to the pilot OFDM symbol, the frequency domain channel information of the data OFDM symbol can be obtained without interpolation.

The solution according to the invention has better performance in a channel environment with rapidly changing and high delay. Specifically, compared to the ideal channel estimation, when the number of cut paths is 32, the performance loss in the channel estimation of the vehicle A channel at 30 km per hour is less than 0.3 dB, which is shown in FIG. 17; In channel estimation of vehicle A channel at 60 km per hour, the performance loss is less than 1.1 dB, which is shown in FIG. 18; Even when the number of cut paths is 160, the performance loss in the channel estimation of the vehicle B channel at 30 km per hour is less than 0.7 dB, which is shown in FIG.

The foregoing is merely exemplary embodiments of the present invention and is not intended to limit the present invention, and various other modifications, equivalent substitutes and modifications within the scope and spirit of the present invention are within the scope of the present invention. It is intended to be included.

Claims (13)

A method for channel estimation in an orthogonal frequency division multiplexing (OFDM) system, a. Determining, by the transmitter, a distribution density of pilot OFDM symbols according to a maximum Doppler frequency shift supported by the system, and transmitting a pilot OFDM symbol and a data OFDM symbol based on the distribution density of the pilot OFDM symbols; And b. Estimating, by the receiver, frequency domain channel information of data OFDM symbols according to the received pilot OFDM symbols Channel estimation method comprising a. The method of claim 1, In step a, determining the distribution density of the pilot OFDM symbols according to the maximum Doppler frequency shift, The number of data OFDM symbols between neighboring pilot OFDM symbols is given by

Determining according to, Where n is the number of data OFDM symbols between neighboring OFDM symbols, T _d is the duration occupied by one data OFDM symbol, and f _{d , max} is the maximum Doppler frequency shift supported by the system Estimation method. The method of claim 1, Step a is The relation between the length Np, data of the data portion of the pilot OFDM symbol and the length Nd.data of the data portion of the data OFDM symbol is expressed as follows.

And setting according to the channel estimation method. The method of claim 1, Step a further includes setting a length of the cyclic prefix portion of the pilot OFDM symbol longer than the length of the cyclic prefix portion of the data OFDM symbol. The method of claim 1, Step b, b11. Obtaining, by the receiver, a time domain channel response of the pilot OFDM symbol according to the received time domain pilot OFDM symbol; b12. Extracting the time domain channel information of the pilot OFDM symbol according to the time domain channel response of the pilot OFDM symbol; And b13. Estimating frequency domain channel information of the data OFDM symbol according to the time domain channel information of the pilot OFDM symbol Channel estimation method comprising a. The method of claim 5, Step b11 is, b111. Obtaining the received frequency domain signal of the pilot OFDM symbol in accordance with the received time domain pilot OFDM symbol; b112. Obtaining a frequency domain channel response of the pilot OFDM symbol according to the received frequency domain signal of the pilot OFDM symbol and the frequency domain signal of the pilot OFDM symbol transmitted by the transmitter; And b113. Obtaining an inverse Fourier transform on the frequency domain channel response of the pilot OFDM symbol to obtain a time domain channel response of the pilot OFDM symbol Channel estimation method comprising a. The method of claim 5, In step b12, extracting the time domain channel information of the pilot OFDM symbol according to the time domain channel response of the pilot OFDM symbol, Determining a truncation range in accordance with the time delay spread supported by the system; Obtaining time domain channel values within the truncation range from the time domain channel response of the pilot OFDM symbol obtained in step b11; And Replacing truncated time domain channel values with zeros Channel estimation method comprising a. The method of claim 5, In step b12, extracting the time domain channel information of the pilot OFDM symbol according to the time domain channel response of the pilot OFDM symbol, Determining one or more of one of the most robust paths of time domain channels through analysis of the time domain channel response of successive pilot OFDM symbols; Selecting a time domain channel value corresponding to the most robust paths; And Replacing non-selected time domain channel values with zeros Channel estimation method comprising a. The method of claim 5, In step b12, extracting the time domain channel information of the pilot OFDM symbol according to the time domain channel response of the pilot OFDM symbol, Determining a truncation range by analyzing the time domain channel response of successive pilot OFDM symbols; Selecting time domain channel values within the truncation range; And Replacing non-selected time domain channel values with zeros Channel estimation method comprising a. The method of claim 5, Step b13, Obtaining, by the receiver, time domain channel information of a data OFDM symbol by taking an interpolation estimate of time domain channel information of neighboring pilot OFDM symbols; And Obtaining corresponding frequency domain channel information by performing inverse Fourier transform on the time domain channel information of the data OFDM symbol Channel estimation method comprising a. The method of claim 10, Taking an interpolation estimate for time domain channel information of the neighboring pilot OFDM symbols, Taking a (2l-1) th order Logarithmic Lagrange interpolation for the interpolation estimation. The method of claim 5, Step b13, Obtaining, by the receiver, corresponding frequency domain channel information according to the obtained time domain channel information of a pilot OFDM symbol; And Obtaining frequency domain channel information of the data OFDM symbol by taking an interpolation estimate on the frequency domain channel information of the neighboring pilot OFDM symbols Channel estimation method comprising a. The method of claim 10 or 12, Taking an interpolation estimate for time domain channel information of the neighboring pilot OFDM symbols, Taking (2l-1) th order Lagrangian interpolation or first order Lagrangian interpolation.

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